Electric condenser and method of constructing the same.



G. HONOLD.

ELECTRIC CONDENSER AND METHOD OF GONSTRUGTING THE SAME.

APPLICATION FILED SEPT. 25, 1911.

1,094,71 8.. Patented A r. 28, 1914.

IAJ/EFJTU 6027/0 HOOO/a UNITED STATES PATENT OFFICE.

GO'ITLOB I-IONOLD, OF STUTTGAR'I, GERMANY, ASSIGNOR TO THE FIR-M OF ROBERT BOSCH, OF- STUTTGART, GERMANY. I

ELECTRIC CONDENSER AND METHOD OF CONSTRUCTING THE SAME.

Specificationof Letters Patent.

Patented Apr. 28, 1914.

Application filed September 25, 1911. Serial No. 651,118.

declare the following to be a full, clear, and

exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The invention relates to a method for the production of electric condensers, and more particularly to the production of the kind of condensers employed in connection with electric igniting machines for internal combustion engines, wherein it is of special importance that the condenser should have the maximum electrical capacity for the space occupied, and that the condenser shall present a mass so firm and rigid that it may be connected up mechanically with the other parts of the machine, and will constitute a homogeneous structural element of the device. Heretofore, condensers designed esspecially to fulfil these requirements employed an insulating material having the highest possible dielectric constant, the insulating material being formed into sheets as thin as possible and being united to the alternately disposed layers of metal by means of a suitable adhesive. Split mica sheets were commonly used for the insulating material and shellac for the adhesive, the shellac being introduced in a thin layer between the plates of mica and the metal layers, and the whole being then heated to the melting temperature of the shellac. Although mica has a high dielectric constant, nevertheless, the dimensions of a condenser constructed in this manner cannot be reduced to the desired extent and often exceed the allowable limit for the required electrical capacity, because it is not feasible to ,split the mica into sufficiently thin laminae. As

a result of this limitation it has been proposed to use paper or some other fibrous material for the insulating, and to coat or saturate the material with an adhesive having goodv electrical insulating properties. Disks of the saturated insulating material and alternately disposed metal layers were built up into a suitable form and the Whole was heated to-the melting .point of the ad hesive, until the layers became united.

However, this construction is not entirely satisfactory for the present purpose, because the heating operation, besides introducing a considerable inconvenience and added cost in the production of the condensers in large quantities, has the further defect that if the adhesive is made. very thin, it distributes itself unevenly when it is in the liquid state and weak spots remain in the insulation.

In accordance with the present invention, it is possible, on the one hand, to make the insulating layers extraordinarily thin and.

thereby to utilize the available space as completely as possible, and, on the other hand, to avoid the employment of heat. To this end, the layers of metal are separated and insulated from one another by extremely thin pliant but tough and cohesive layers of insulating material, and the whole is firmly united, and the layers brought into intimate surface contact by cold pressure. For the purpose of making such layers of insulating material, I take advantage of the properties of those varnishes which form, after being completely dried, a pliant layer with smooth surface, and capable of adhering closely to the metal layers against which they are pressed. For this purpose I have found practically available insulating solutions produced from an admixture of drying oils, such as Wood oil, linseed oil, or the ,like, with difliculty fusible fossil copals,

such as Benguela, Brazil or Kauri, and the like, such mixture being oxidized by boiling at high temperatures, assist-ed by the injection of hot air, and the thickly fluid mass thus obtained being dissolved in a suit-able solvent, such as turpentine, benzin, benzol, or the like. From this solution, suitable insulating layers may be formed in different ways. It is feasible to spread the sclution thinly upon the surfaces of the metal layers themselves, or the layers of insulation may be formed by saturating very thin paper or like fibrous material with the solution and thereupon completely drying. In such case, the paper or other fibrous material is not,.. as in the methods heretofore known, wherein the substance servlng as the insulater is made fluid by heating, relied upon to maintain the metal layers apart from each other to thereby assist the insulation,

but it is employedexclusively as a carrier for :propuring an insulating layer in suificiently thin sheets in the first instance- The layers of insulating material thus obtained are packed together alternately with metal foil and exposed cold to the pressure which is made sufficiently high and is maintained for a sufiicient length of time to unite the individual layers in a firm mass. In this way, there is obtained a complete union of the layers of insulation and the layers of metal to such an extent that a condenser constructed in accordance with the process will present a mass having substantially the rigidity of wood. The highly polished surface of the dried layer of insulating material thus produced insures a completely uniform contact over the entire surface of the metal layers, and produces at a relatively low pressure, so close an adhesion that the layers of the completed condenser cannot be separated from'each other at all, or only with great difficulty, without tearing.

The complete uniformity of thickness of the insulating layer ofi'ers no weaker places of any kind on the metal, and the consequence is that in addition to the great advantage that no heating is required in the production of such a condenser, the possibility is presented of making the insulating layers materially thinner than has been pos-. sible with the methods of production heretofore employed. This is so much sothat condensers may be made which with the same dimensions, possess more than double the capacity of mica condensers.

The method may be carried out by superposing upon each other the metal foil and the insulating layers, cut out in disks of the desired form, and introducing the mass into I a press which gives the necessary pressure,

and then providing the bodies thus produced with metal sheathings to which the leadinginv wires may be connected. Or any well known form of coil condenser may be constructed by winding together alternate layers of metal and the described insulation. By employing thin and tough paper, and taking advantage of the elastic property of the dried insulating solution so that the paper saturated with the solution is flexible and can be bent without cracking, coil condensers can be constructed without employing special pressure rolls for pressing the layers of metal and insulating material together at the advancing point'of union. It sufiices to maintain the strips of the impregnated insulating material under a tension, during the winding operation, which does not exceed the limit of their elasticity. They then exert in winding, a further small radial pressure upon each other,but as long as the limit of elasticity is not exceeded,

this pressure continues and it suflices for; the production of the necessary adhesion.

This effect is at the same timemade possible by the fact that the smooth surface of the insulating materialatfords an even and intimate contact of the two surfaces. Although it is possible to thus construct coil condensers without the use of pressure rolls, it will be understood, of course, that the e1nployment of such rolls is not excluded.

Condensers constructed in accordance with the invention may very conveniently be made by winding the layers upon an elongated support, so that the completely wound condenser becomes elliptical, and in such case, it is peculiarly advantageous to apply the insulating material directly upon the strips of metal, so that no separate support is necessary for the insulation.

In the accompanying drawings, illustrating a condenser constructed in accordance with my invention, Figure 1 shows an elliptical coil-wound condenser in the process of construction; Fig. 2 is a face view of the completed condenser; Fig. 3 is a perspective view of it; Fig. 4 shows a cylindrical condenser built up of alternate disks of metal and insulating material; and Fig. 5 shows, in perspective, a longitudinal section illustrating the building-in of the condenser with the armature of an ignition machine.

The condenser shown in the process of construction in Fig. 1, and completed in Figs. 2 and 3, is made by simultaneously winding up into the form of an elliptical coil, two strips of metal a and two interposed strips of paper m, impregnated with the above-described insulating solution, and thoroughly dried. The strips may be subjected to the action of pressure rolls to press the layers together at the advancing point of union, or the insulating strips may be kept under a tension which does not exceed their limit of elasticity, as above described.

The cylindrical condenser of Fig. 4 is made by piling upon one another, alternate disks of metal and the above-described insulating material, and subjecting the whole Into this recess, an 5.

wall of the housing and are thereby con- 7 ducti'vely connected with the latter and consequently, with the body of the armature. The housing is closed by an elliptically formed cover 03, the periphery of which is spaced apart from the edge of the housing,

and is separated therefrom by insulation n. Th1s cover is in contact with the other alternate layers and serves to conductively connect them, and it is insulated from the armature core by the insulation n. For the purpose of securing the cover in place, it is preferably provided with a projection e which extends into the space formed in the middle of the condenser, is insulated therefrom as shown, and is held in place by a screw bolt f having the washer g of insu lating material and the nut it. Such a condenser as compared with the ordinary forms heretofore employed, has the advantage that it can be built upon the armature of an ignition machine, in a very secure and simple manner, without being provided with metal coverings for holding it together, and furthermore, in consequence of its elliptical form, the otherwise necessary precautions against unintentional shifting, are rendered superfluous. I

Having thus described my invention, what I claim is:

l. The method of manufacturing electric condensers which consists in interposing between layers of conducting material, thin and pliant but cohesive dried layers of an insulation solution, and causing the whole to firmly unite in even surface contact by cold pressure.

2. The method of manufacturing electric condensers which consists in interposing between layers of conducting material, previously dried thin layers of a solution containing diflicultly fusible nfossil copal, a drying oil, and a suitable solvent; and causing the whole to firmly unite in even surface contact by cold pressure.

3. The method of manufacturing electric condensers which consists in interposing between layers of conducting material, thin dried layers of fibrous material impregnated with a solution containing difiicultly fusible fossil copal, a self-drying oil, and a suitable solvent; and causing the Whole to firmly unite in even surface contact by cold pressure.

- 4:. The method of manufacturing coilwound electric condensers which co sists in winding on a suitable core, alternate y disposed strips of metal and thin and pliant but cohesive dried layers of an insulation solution; and applying sufiicient cold pressure to said strips during the winding to firmly unite them in evensurface contact.

5. The method of manufacturing coilwound electric condensers which consists in winding on a suitable core alternate layers of metal and of a fibrous material impregnated with a solution containing difiicultly fusible fossil copal, a self-drying oil and a suitable solvent, and subsequently dried; and maintaining the said strips of fibrous material under tension during the winding operation to thereby apply suflicient cold pressure to firmly unite the whole in even surface contact.

6; An electric condenser comprising layers of conducting material separated and insulated from one another by thin and pliant but cohesive layers of a solution containing difiicultly fusible fossil copal, a drying oil and a suitable solvent, dried prior to assembling the condenser.

In testimonv whereof I affix my signature in presence of two witnesses.

GOTTLOB HONOLD. Witnesses:

REINHOLD ELWERT, WALTHER STEINOKE. 

